In the field of computer systems there is a need to obtain the time of day (“TOD”). Unfortunately, the quality of the results in terms of accuracy and resolution is often less than optimum. Even when interpolation is used, as on recent versions of Linux there may be a significant short-term skew error. Furthermore, corrections may involve discontinuities or jumps. The way the high-resolution counter typically is used sometimes causes a sawtooth pattern when the system clock is compared to a smooth and accurate reference clock.
Many systems (other than IBM System Z) use system calls to obtain the TOD and the quality of the result in terms of accuracy and resolution is often not very good.
Even when interpolation is used, as on recent versions of Linux, there may be significant short-term skew error, and corrections may involve jumps.
The high-resolution counter typically used for interpolation could be used in a way that avoids inadequacies such as a saw tooth pattern when the system clock is compared to a smooth and accurate reference clock.
Other relevant background information can be found in the following patent documents:
“Clock filter dispersion”, by Scott Carlson, Michel Hack and Li Zhang, filed 9 Sep. 2005 in the USPTO as application Ser. No. 11/223,878, assigned to IBM Corporation; and
“Use of T4 timestamps to calculate clock offset and skew”, by Scott Carlson, Michel Hack and Li Zhang, filed 9 Sep. 2005 in the USPTO as application Ser. No. 11/223,577, assigned to IBM Corporation.